Construction And Working Of Permanent Magnet Moving Coil Instrument Pdf


By Gabriel H.
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25.03.2021 at 15:38
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construction and working of permanent magnet moving coil instrument pdf

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There are different electrical machines are used in the ship so that it can travel from place to another safely as well as capably.

It is one of the simple and most used instruments on board with sophisticated names. They are used on board to assist in regular maintenance of electrical equipment or when precise measurements are required. It is a simple machine that creates stationary magnetic fields with two powerful permanent magnets. A PMMC Equipment consists of two main parts; moving coil and a permanent magnet along with other parts. These parts are explained below:.

PMMC Instrument Working Principle | Permanent Magnet Moving Coil Instrument

Hi friends, in this article, I am going to discuss about moving coil instrument working principle and other related information. You will appreciate my effort, I hope so. The simple view of construction of moving coil instrument is shown in the figure. It consists of a powerful permanent shoe magnet.

A light rectangular coil of many turns of fine wire is wound on a light aluminum former. An iron core is inserted inside the coil to reduce reluctance for the magnetic lines of force.

The coil is mounted on the spindle and acts as the moving element. Two phosphor bronze spiral hairsprings are attached to the spindle. The springs provide the controlling torque as well as they act as incoming and outgoing leads for the current.

Eddy current damping is provided by the aluminum former. The basic moving coil instrument working principle is that when a current carrying conductor is placed in a magnetic field, a mechanical force is exerted on the conductor. The basic principle can also be stated that when a field resultant magnetic field produced by the movable current carrying coil tries to come in line with the main field produced by the permanent magnet , thus a deflecting torque is developed.

By the production of deflecting torque, the pointer deflects over the scale. When the moving coil instrument is connected in the circuit, the operating current flows through the coil which is mounted on the spindle. Since the coil is placed in the strong field of permanent magnets, a force is exerted on the current carrying conductors of the coil which produces deflecting torque.

Thus the pointer attached to the spindle in deflected over the calibrated scale. If the current in the coil is reversed, the direction of deflecting torque will be reversed because of the field produced by the permanent magnets remains the same. This will give a wrong direction of rotation thus the instrument cannot be used on AC, permanent magnet moving coil instruments can be used for the measurement of DC only.

Magnets: In order to have permanence in magnetism, magnets are aged by heat and vibration treatment. This process results in loss of initial magnetism but that remains is strongly held. Springs: The weakening of springs with time can be reduced by careful use of material and pre-aging during manufacture. However, the effect of the weakening of springs on the performance of the instrument is opposite to that of magnets. The weakening of magnets tends to decrease the deflection for a particular value of current while the weakening of springs tends to increase the deflection.

Thus the net effect on the average is to increase the deflection by about 0. Moving Coil : The moving coil of measuring instrument is usually wound with a copper wire having a temperature coefficient of 0. When the instrument is used as a micro-ammeter or a milli-ammeter and moving coil is directly connected to the output terminals of the instruments, the indication of the instrument for a constant current would decrease by 0.

In case of moving coil instrument, is used as a voltmeter a large series resistance of negligible temperature coefficient made of material like manganin is used. This eliminates the error due to temperature.

This is because of copper coil forms a very small fraction of the total resistance of the instrument circuit and thus any change in its resistance has a negligible effect on the total resistance. In a situation when the instrument current range is extended by using a shunt is, however, different. The main source of error, in this case, is due to the relatively larger change in the resistance of the copper moving coil as compared to that of manganin shunt.

This happens because copper has a much higher resistance temperature coefficient as compared to manganin. This swamping resistance is also used for the final calibration of the ammeter. Thanks for reading about moving coil instrument working principle. If you have any question about this topic, you can ask me in the comment section given below.

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Permanent Magnet Moving Coil or PMMC Instrument

Electrical Academia. Figure 1 shows the basic construction of a PMMC instrument. A moving-coil instrument contains principally of a permanent magnet to offer a magnetic field and a small lightweight coil pivoted within the field. A soft iron core is included between the poles of the magnet so that the coil rotates in the narrow air gap between the poles and the core. The resulting deflection of the coil is indicated by a pointer that moves over a calibrated scale. In addition to a deflecting force provided by the coil current and the field from the permanent magnet, a controlling force is needed.

It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet. The moving coil and permanent magnet are the main part of the PMMC instrument. The parts of the PMMC instruments are explained below in details. Moving Coil — The coil is the current carrying part of the instruments which is freely moved between the stationary field of the permanent magnet. The current passes through the coil deflects it due to which the magnitude of the current or voltage is determined. The coil is mounted on the rectangular former which is made up of aluminium.

The PMMC works on the electromagnetic effect. A permanent magnet is used to produce magnetic flux and a coil that carries the current to be measured moves in this field. As the pointer is connected to the coil it gets deflected in proportion with the current. When a current carrying conductor placed in the magnetic field experiences a force. It is given by the expression is given below,. The basic construction of PMMC is shown in above fig. This light rectangular coil carries the current to be measured.


The PMMC instrument working principle is when the torque is applied to the moving coil that is placed within the permanent magnet field, and then it gives a.


PMMC Instruments – Construction and Working Principle

An ammeter from ampere meter is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes A , hence the name. The ammeter is usually connected in series with the circuit in which the current is to be measured. An ammeter usually has low resistance so that it does not cause a significant voltage drop in the circuit being measured.

Several electrical machines and panels are fitted on board so that the ship can sail from one port to another, safely and efficiently. The electrical machinery and system require scheduled maintenance and checks to avoid any kind of breakdown during sailing.

What is PMMC Instrument : Construction & Its Working

Facebook Twitter. The permanent magnet moving coil instrument is the most accurate type for dC measurements. Working principle of pmmc instrument is the same as that of the d'Arsonval type of galvanometers, the difference being that direct reading instrument is provided with a pointer and a scale. Construction of pmmc instruments:. The general constructional features of pmmc instrument are shown in below figure:. Moving coil: The moving coil is wound with many turns of enamelled or silk covered copper wire.

Moving Coil:. The moving coil made up of copper is wound with many turns on the rectangular Aluminum former. This Aluminum former is pivoted on the jewelled bearing.


The permanent magnet moving coil instruments are most accurate type for direct current As the coil is moving and the magnet is permanent, the instrument is called The cost is high due to delicate construction and accurate machining.


Advantages and Disadvantages Moving Coil Instruments

Впервые за многие годы коммандер почувствовал себя молодым. Его мечта была близка к осуществлению. Однако, сделав еще несколько шагов, Стратмор почувствовалчто смотрит в глаза совершенно незнакомой ему женщины. Ее глаза были холодны как лед, а ее обычная мягкость исчезла без следа. Сьюзан стояла прямо и неподвижно, как статуя. Глаза ее были полны слез. - Сьюзан.

 Это была шутка, Мидж.  - Но он знал, что сказанного не вернешь. ГЛАВА 62 Коммандер и Сьюзан стояли у закрытого люка и обсуждали, что делать. - Итак, внизу у нас погибший Чатрукьян, - констатировал Стратмор.  - Если мы вызовем помощь, шифровалка превратится в цирк. - Так что же вы предлагаете? - спросила Сьюзан. Она хотела только одного - поскорее уйти.

Именно он принимал ее на работу, именно он сделал АНБ для нее родным домом. Когда десять лет назад Сьюзан поступила в агентство, Стратмор возглавлял Отдел развития криптографии, являвшийся тренировочной площадкой для новых криптографов, криптографов мужского пола. Хотя Стратмор терпеть не мог выделять кого-нибудь из подчиненных, он с особым вниманием относился к своей единственной сотруднице.

Так вот почему Дэвид отложил поездку в Стоун-Мэнор. - Сегодня утром я послал за ним машину. Он сказал, что позвонит тебе перед вылетом. Прости, я думал… - Зачем вы послали его в Испанию.

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Construction. A coil of thin wire is mounted on an aluminium frame (spindle) positioned between the poles of a U shaped permanent.

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